The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of manufacturing a highly integrated semiconductor device (e.g., vertical transistors) and improving the operating characteristic and yield of the semiconductor device.
In general, a semiconductor is a material classified according to its electrical conductivity and belongs to an intermediate region between a conductor and a nonconductor. The semiconductor has a property that is similar to that of the nonconductor in a pure state, but has an increasing electrical conductivity with the addition of impurities or other control. Such a semiconductor is used to produce semiconductor elements, such as transistors, by adding impurities and connecting conductors thereto. A device fabricated using the semiconductor elements and configured to have a variety of functions is called a semiconductor device. A representative example of the semiconductor device may include a semiconductor memory device.
The semiconductor memory device includes a number of unit cells each comprising a capacitor and a transistor. The capacitor is used to temporarily store data. The transistor is used to transfer data between a bit line and the capacitor in response to a control signal (a word line). The transistor is divided into three regions; a gate, a source, and a drain. Electric charges are moved between the source and the drain in response to the control signal input to the gate. The movement of electric charges between the source and the drain is carried out through a channel region.
In the case where a typical transistor is formed in a semiconductor substrate, a gate is formed in the semiconductor substrate, and a source and a drain are formed on both sides of the gate by doping impurities. In this case, a channel region of the transistor is formed between the source and the drain under the gate. The transistor having this horizontal channel region occupies a certain area of the semiconductor substrate. Accordingly, in the case where a complicated semiconductor memory device is fabricated, it is difficult to reduce the area of the semiconductor memory device because of a number of transistors included in the semiconductor memory device.
If the area of the semiconductor memory device is reduced, productivity can be improved because the number of semiconductor memory devices that can be produced per wafer can be increased. Several methods are being proposed in order to reduce the area of the semiconductor memory device. One of the methods is to use a vertical transistor having a vertical channel region instead of a conventional horizontal transistor having a horizontal channel region.